Underwater power generators, e.g. for generating electrical power, and associated turbine units are known.
WO 03/029645 A1 (also by the present Applicant) discloses a power generator, such as an electrical power generator, comprising at least one underwater turbine unit including a housing having a liquid flow channel therethrough and at least one turbine means mounted in the flow channel for rotation in response to liquid flow through the channel. The turbine unit also comprises a pump means operatively coupled to the turbine means. The turbine unit provides a turbine unit part releasably mountable in the turbine unit, the part including at least one of the at least one turbine means and the pump means. In the disclosed embodiments the turbine unit part also comprises at least part of the flow channel.
The content of the aforementioned document is incorporated herein by reference.
Known tidal or current electrical power generators seek to address a need for increasing energy requirements in an environmentally friendly way. However, known generators suffer from a number of problems, e.g. relatively low efficiency of conversion of tidal and/or current flow to electrical energy.
So-called “symmetrical” aerofoils are known, and are employed for the stabilising surfaces of aircraft, such as the fin and tailplane, and also for wings of highly aerobatic aircraft which require the “lift” force to be high in both positive and negative directions. These aerofoils have zero “camber” or, in other words, a straight mean line which is clothed with a streamline form symmetrical about the mean line. Such a streamline form is asymmetrical fore and aft, with a blunt leading edge and a sharp trailing edge. This form has also been used for ships hulls. Conventionally, the leading edge or “entry” has been easier to design than the rearward curves or “run” of a ship's hull. This reflects the generally accelerating flow with falling pressure at the front, whereas the flow must decelerate towards the trailing edge and the rising pressure there tends to force a “separation” of the flow from the surface. The resulting chaotic wake gives very high drag, and where aircraft wings are concerned, a collapse of lift.
A wide variety of aerofoil forms have been developed and investigated throughout the last century. Systematic design philosophies were developed by NACA in particular, using families of streamline shapes to clad camber lines of varying curvature. Even when the camber is zero and the camber line just a straight line, the empirical streamline shapes vary in the position of maximum thickness and the relative size of the leading edge.
It is an object of at least one embodiment of at least one aspect of the present invention to obviate or at least mitigate one or more problems in the prior art.
It is a further object of one or more embodiments of at least one aspect of the present invention to provide an underwater turbine unit which, in use, is driven by tidal and/or current flow, and which can preferably operate in ebb and/or flood tides without a need for movement or realignment into a tidal flow direction.
It is a yet further object of at least one embodiment of at least one aspect of the present invention to provide a power generator apparatus or farm which is substantially or wholly underwater, thereby minimising environment impact.
It is a still further object of at least one embodiment of at least one aspect of the present invention to provide a power generator apparatus wherein maintenance may be carried out without diver or ROV (Remotely Operated Vehicle) intervention.
It is a further object of at least one embodiment of at least one aspect of the present invention to provide an aerofoil form which is capable of relatively high lift and low drag with flow approaching from either direction.
It is a further object of at least one embodiment of at least one aspect of the present invention to provide an aerofoil suited to use in a turbine for tidal or current energy extraction, e.g. where reversing tides present flow from substantially opposing directions.
It is a further object of at least one embodiment of at least one aspect of the present invention to provide an aerofoil form suited to energy extraction where flow periodically changes direction.
It is a further object of at least one embodiment of at least one aspect of the present invention to provide a bi-directional aerofoil form with relatively low drag and good structural rigidity, tolerant of a relatively wide range of incident flow angles.
It is a further object of at least one embodiment of at least one aspect of the present invention to provide a design procedure teaching for generating a family of aerofoils having their maximum thickness tailored to the structural duty, by scaling of a basic profile.
It is a further object of at least one embodiment of at least one aspect of the present invention to provide a teaching for a procedure for generating a family of aerofoils whereby a novel basic aerofoil is designed to give favourable velocity distributions at a required thickness as a basis for a bi-symmetrical reflected profile.